1. Field of the Invention
The present invention relates to subsurface well completion equipment and, more particularly, to apparatus and related methods for using a small number of hydraulic control lines to operate a relatively large number of downhole devices.
2. Description of the Related Art
The late 1990's oil industry is exploring new ways to control hydrocarbon producing wells through a technology known as "Intelligent Well Completions", or "Smart Wells", the definition of which is hereinafter described. Because of hostile conditions inherent in oil wells, and the remote locations of these wells--often thousands of feet below the surface of the ocean and many miles offshore--traditional methods of controlling the operation of downhole devices are severely challenged, especially with regard to electrical control systems. Temperatures may reach 300-400 degrees F. Brines used routinely in well completions are highly electrolytic, and adversely affect electric circuitry if inadvertently exposed thereto. Corrosive elements in wells such as hydrogen sulfide, and carbon dioxide can attack electrical connections, conductors, and insulators and can render them useless over time. While the volume and production rate of hydrocarbons in a subterranean oil reserve may indicate an operational life of twenty or more years, the cost to mobilize the equipment necessary to work over and make repairs to deepwater offshore and subsea wells may run into the tens of millions of dollars. Therefore, a single workover can cost more than the value of the hydrocarbons remaining in the subterranean formation, and as such can result in premature abandonment of the well, and the loss of millions of dollars of hydrocarbons, should problems requiring workover occur.
For these reasons, reliability of systems operating in oil wells is of paramount importance, to the extent that redundancy is required on virtually all critical operational devices. Traditionally, electrical devices used in oil wells are notoriously short lived. Vibration, well chemistry, heat and pressure combine and attack the components and conductors of these electrical devices, rendering them inoperative, sometimes in weeks or months, often in just a year or two. Because of the need for such high levels of reliability, there is a need to reduce the reliance on, or eliminate altogether, electrical control systems in wells. Yet there is a need to control and manage multiple devices and operations in wells with a high degree of reliability.
Well known in the industry is the method of controlling devices in wells utilizing pressurized hydraulic oil in a small diameter control line, extending from a surface pump, through the wellhead, and connecting to a downhole device, such as a surface controlled subsurface safety valve (SCSSV) Such a configuration is shown in U.S. Pat. No. 4,161,219, which is commonly assigned hereto. Pressure applied to the control line opens the SCSSV, and bleeding off said pressure allows the SCSSV to close, blocking the flow of hydrocarbons from the well. Hydraulic control has long been used in this critically important, and highly regulated application because of its high degree of reliability, primarily because: 1) the metallurgy of control lines and its connective fittings have been developed to be resistant to the corrosive elements/conditions in wells; and 2) the hydraulic oils used are essentially incompressible, and are not significantly affected by the wellbore's temperature and pressure.
Well known and for many years in the oil industry, downhole devices are manipulated by wireline (or slickline), whereby the well is taken out of production, the well is "killed" by means of a heavy brine fluid, the wellhead is removed and a lubricator is installed. Wireline tools are inserted in the well through the lubricator and suspended and lowered by a heavy gauge wire to the area of the well where remediation is required. Unfortunately, in the case of subsea wells, wireline operations are difficult in that a ship must be mobilized and moved over the wellhead before said wellhead can be removed, a lubricator installed, and the wireline work begun. As the ocean depth over the well increases, this task becomes exponentially more difficult and expensive.
Another device commonly used in well completions is known as a wellhead. The wellhead is positioned at the uppermost end of the well, and is essentially the junction between the subsurface portion of the well, and the surface portion of the well. In the case of subsea wells, the wellhead sits on the ocean floor. The wellhead's purpose is to contain the hydrocarbons in the well, and direct said hydrocarbons into flow lines for delivery into a transportation system. A common wellhead is shown in U.S. Pat. No. 4,887,672 (Hynes). If hydraulic control lines are to be used downhole, often the operator will specify a number of ports to be built into the wellhead, most commonly one or two. After the wellhead is built it may be difficult or impossible for additional ports to be added to the wellhead, owing to the thickness of the metal, or the proximity to other appurtenances. Additional hydraulic ports can be expensive in any case, and having many additional ports added can be cumbersome.
The definition of "Intelligent Well Completions" or "Smart Wells" is used for a combination of specialized equipment that is placed downhole (below the wellhead), which enables real time reservoir management, downhole sensing of well conditions, and remote control of equipment. Examples of "Intelligent Well Completions" are shown in U.S. Pat. No. 5,207,272 (Pringle et al.), U.S. Pat. No. 5,226,491 (Pringle et al.), U.S. Pat. No. 5,230,383 (Pringle et al.), U.S. Pat. No. 5,236,047 (Pringle et al.), U.S. Pat. No. 5,257,663 (Pringle et al.), U.S. Pat. No. 5,706,896 (Tubel et al.), U.S. patent application Ser. No. 08/638,027, entitled "Method and Apparatus For Remote Control of Multilateral Wells," and U.S. Provisional Patent Application Ser. No. 60/053,620, and are incorporated herein by reference.
In the case of "Intelligent Well Completions," if hydraulic control is the method of choice for the multiplicity for devices in the well, and the hydraulic pressure source emanates from the surface, a large number of ports will be required in the wellhead, and a large number of hydraulic control lines will have to be passed to individual hydraulically actuated components in the wellbore. Hydraulically-actuated components may include SCSSVs, sliding sleeves, locking or latching devices, packers (or packer setting tools), expansion joints, flow control devices, switching devices, safety joints, on/off attachments or artificial lift devices. Of note are advanced gas lift valves, such as the preferred embodiments shown in U.S. Provisional Patent Application Ser. No. 60/023,965. Because so many items in such a well are in need of individual control, the bundle of control lines to perform work in the well can become difficult and unworkable.
Because of the aforementioned problems, there is a need for a hydraulic control system which can control a multiplicity of downhole devices in a well, perform complex operations (usually reserved for workovers) on the fly, without lengthy and expensive well shut-ins, and with a minimum number of control lines from the surface. Further, there is a need to have a system which is resistant to well conditions, and one which will be operationally reliable for many years. There is a need for a system to approximate the computational and operational complexity of electric control systems, with only a few input signals, by use of hydraulic fluid flow, hydraulic fluid pressure oscillation, hydraulic fluid pressure, and proximity sensors to report control valve position, and coupled to a computer at the surface for simplified control and user interface.